login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A303659 Numbers k such that the average of greatest prime factors of all positive integers <= k is an integer. 1
2, 5, 6, 24, 27, 28, 79, 1171, 1901, 1932, 7845, 19152, 360698, 649358, 1731441, 1979944, 30658517, 34337898, 400114748, 412626117, 3738454462, 7725156081, 97366414806, 129951504625, 290788509485 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Numbers k such that (k - 1) | (A046670(k) - 1).
Numbers k such that (k - 1) | A088822(k).
a(26) > 10^12. - Giovanni Resta, May 05 2018
LINKS
Eric Weisstein's World of Mathematics, Greatest Prime Factor
EXAMPLE
6 is in the sequence because (gpf(2) + gpf(3) + gpf(4) + gpf(5) + gpf(6))/5 = (2 + 3 + 2 + 5 + 3)/5 = 3 is an integer.
PROG
(PARI) isok(n) = (n>1) && !(sum(k=2, n, vecmax(factor(k)[, 1])) % (n-1)); \\ Michel Marcus, Apr 29 2018
(PARI) lista(nn) = {s = 0; for (n=2, nn, s += vecmax(factor(n)[, 1]); if (! (s % (n-1)), print1(n, ", ")); ); } \\ Michel Marcus, Apr 29 2018
CROSSREFS
Sequence in context: A136324 A128367 A178924 * A250546 A137067 A214200
KEYWORD
nonn,more
AUTHOR
Ilya Gutkovskiy, Apr 28 2018
EXTENSIONS
a(13)-a(18) from Michel Marcus, Apr 29 2018
a(19)-a(25) from Giovanni Resta, May 05 2018
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 25 16:50 EST 2024. Contains 370332 sequences. (Running on oeis4.)